TWI883379B - Etching of metal oxides using fluorine and metal halides - Google Patents

Abstract

Embodiments of this disclosure provide methods for etching oxide materials. Some embodiments of this disclosure provide methods which selectively etch oxide materials over other materials. In some embodiments, the methods of this disclosure are performed by atomic layer etching (ALE). In some embodiments, the methods of this disclosure are performed within a processing chamber comprising a nickel chamber material.

Description

Etching metal oxides using fluorine and metal halides

Embodiments of the present disclosure generally relate to methods for selective atomic layer etching of metal oxides using fluorine and metal halide sources. In particular, some embodiments of the present disclosure relate to methods for selective atomic layer etching of metal oxides by fluorination and removal with metal halides. Some embodiments of the present disclosure provide alternative fluorine sources for HF, which may be undesirable from a manufacturing standpoint.

As semiconductor devices continue to increase in complexity both in design and in material composition, the selective removal of materials has become critical to the continued scaling and improvement of semiconductor devices.

Selective atomic layer etching (ALE) has emerged as a precise etching method that exploits self-limiting surface reactions. Selective ALE of metal oxides ( _MOx ) is particularly important for many semiconductor technologies, but can be difficult to accomplish due to the inherent stability of these oxide materials. One such example is the selective removal of _HfO2 during recess etching of high-k metal gate structures.

Selective removal of metal oxides and nitrides is critical to continued miniaturization and optimization in semiconductor manufacturing. While some etch processes exist, these processes are either non-selective or rely on HF as the fluorine source. HF is toxic and poses disposal issues during manufacturing. It would be desirable to have alternative fluorine sources for metal oxide etching that avoid these concerns for widespread adoption in etch processes.

Therefore, new sources of fluorine and metal halides are needed for the selective removal of metal oxides and metal nitrides.

One or more embodiments of the present disclosure relate to an etching process, which includes exposing a substrate surface having an oxide layer thereon to a fluoriding agent to convert a portion of the oxide layer into a fluoride layer, and exposing the fluoride layer to a halogenide etchant to remove the fluoride layer.

Another embodiment of the present disclosure relates to an etching process, the etching process comprising exposing a substrate surface having a hydroxide layer thereon to a fluoriding agent to form a fluoride layer, and exposing the fluoride layer to a halogenide etchant to remove the fluoride layer.

Other embodiments of the present disclosure relate to an etching process, the etching process comprising exposing a substrate surface having an oxide layer and a second material to a fluoriding agent in a processing chamber including a nickel chamber material to selectively convert a portion of the oxide layer into a fluoride layer. The second material comprises one or more of the following: TiN, SiN, TaN, SiO, AlO, LaO, carbon, silicon, or a combination thereof. The fluoride layer is exposed to a halide etchant to remove the fluoride layer.

Before describing several exemplary embodiments of the present disclosure, it should be understood that the present disclosure is not limited to the details of the construction or process steps set forth in the following description. The present disclosure is capable of other embodiments and can be practiced or carried out in various ways.

As used in this specification and the appended claims, the term "substrate" refers to a surface or a portion of a surface on which a process is performed. Those skilled in the art will also understand that, unless the context clearly indicates otherwise, reference to a substrate can also refer to only a portion of a substrate. In addition, reference to etching from or depositing on a substrate can mean both a bare substrate and a substrate on which one or more films or features are deposited or formed.

As used herein, "substrate" refers to any substrate or material surface formed on a substrate on which film processing is performed during a manufacturing process. For example, substrate surfaces on which processing can be performed include materials such as the following: silicon, silicon oxide, strained silicon, silicon on insulator (SOI), carbon doped silicon oxide, amorphous silicon, doped silicon, germanium, gallium arsenide, glass, sapphire, and any other materials, such as metals, metal nitrides, metal alloys, and other conductive materials, depending on the application. Substrates include (but are not limited to) semiconductor wafers. The substrate can be exposed to a pre-treatment process to grind, etch, reduce, oxidize, hydroxylate, anneal, UV cure, electron beam cure and/or bake the substrate surface. In addition to performing film treatments directly on the surface of the substrate itself, in the present disclosure, any film treatment steps disclosed may also be performed on an underlayer formed on the substrate, as disclosed in more detail below, and it is intended that the term "substrate surface" includes the underlayer indicated by the context. Thus, for example, where a film/layer or portion of a film/layer has been removed from the substrate surface, the exposed surface of the newly exposed film, layer, or substrate becomes the substrate surface.

As used in this specification and the appended claims, the terms "precursor," "reactant," "reactant gas," and similar terms are used interchangeably to refer to any gaseous species capable of reacting with a substrate surface.

"Atomic layer etching" (ALE) or "cyclic etching" is a variation of atomic layer deposition in which a surface layer is removed from a substrate. As used herein, ALE refers to etching a layer of material on a substrate surface by sequentially exposing two or more reactive compounds. The substrate or a portion of the substrate is separately exposed to two or more reactive compounds, which are introduced into a reaction zone of a processing chamber.

In a time-domain ALE process, exposure to each reactive compound is separated by a time delay to allow each compound to attach and/or react on the substrate surface and then be flushed from the processing chamber. The reactive compounds are said to be exposed to the substrate sequentially.

In one aspect of a time-domain ALE process, a first reactant gas (i.e., a first reactant or compound A) is pulsed into a reaction zone, followed by a first time delay. Next, a second reactant or compound B is pulsed into the reaction zone, followed by a second delay. During each time delay, a purge gas, such as argon, is introduced into the processing chamber to purge the reaction zone, or otherwise remove any remaining reactive compounds or reaction byproducts from the reaction zone. Alternatively, the purge gas may flow continuously throughout the etching process, such that only the purge gas flows during the time delays between pulses of the reactive compounds. Alternatively, the reactive compound is pulsed until the desired film or film thickness is removed from the substrate surface.

An ALE process that supplies compound A, purge gas, compound B, and purge gas pulses is called a cycle. A cycle can start with either compound A or compound B and continue in that order until a predetermined thickness is removed.

In a spatial ALE process, different portions of a substrate surface (or material on a substrate surface) are simultaneously exposed to two or more reactive compounds such that any given point on the substrate is not substantially exposed to more than one reactive compound simultaneously. As used in this regard, as understood by those skilled in the art, the term "substantially" refers to the possibility that a small portion of the substrate may be simultaneously exposed to multiple reactive gases due to diffusion, and that such simultaneous exposure is undesirable.

In one embodiment of a spatial ALE process, a first reactive gas and a second reactive gas are delivered to the reaction zone simultaneously but separated by an inert gas curtain and/or a vacuum curtain. The substrate moves relative to the gas delivery device so that any given point on the substrate is exposed to the first reactive gas and the second reactive gas.

Some embodiments of the present disclosure relate to methods for etching or removing metal oxides from a substrate surface. Some methods of the present disclosure advantageously utilize fluorinating agents other than HF.

Some methods of the present disclosure advantageously provide methods for selectively removing metal oxide materials in preference to other substrate materials. As used in this regard, the term "selectively removing one film in preference to another film" and similar terms mean removing a first amount from a first surface or material while removing a second amount from a second surface or material, wherein the second amount is less than the first amount, or no film is removed from the second surface. The term "over" as used in this regard does not imply a physical orientation of one surface on top of another, but rather implies a relationship to the thermodynamic or kinetic nature of a chemical reaction at one surface relative to the other.

The selectivity of a process is often expressed as a multiple or ratio of the etch rates between different surfaces. For example, if one surface etches 25 times faster than another surface, the process would be described as having a selectivity of 25:1. In this regard, a higher ratio indicates a more selective process.

One or more embodiments of the present disclosure relate to methods for removing metal oxides. In some embodiments, a substrate including an oxide surface can be treated with a fluorine source (also referred to as a fluoriding agent), then purged, then treated with a metal halide (also referred to as a halide etchant), then purged. The cycle can be repeated to remove a predetermined thickness of metal oxide.

1 to 4A, the method 100 begins at operation 110, where a substrate 600 including an oxide layer 610 is exposed to a fluoriding agent to form a fluoride layer 620. The method 100 continues at operation 120, where the fluoride layer 620 is exposed to a halogenide etchant to remove the fluoride layer 620. Scheme 1 provides an exemplary reaction scheme of the method 100 shown in FIGS. 1 and 4A.

Scenario 1:

Metal oxide + fluorine source → metal fluoride layer (1)

Metal fluoride layer + metal halide → volatile products (2)

In some embodiments, as shown in Scheme 1, oxide layer 610 includes a metal oxide. In these embodiments, fluoride layer 620 can be referred to as a metal fluoride layer. In some embodiments, the metal oxide includes one or more of: tungsten oxide, molybdenum oxide, titanium oxide, or a combination thereof. In some embodiments, the metal oxide includes or consists essentially of tungsten oxide.

As used in this regard, a material consists essentially of a material if, on an atomic basis, it is greater than or equal to about 95%, 98%, 99%, or 99.5% of the material.

The fluorinating agent may include any suitable reactant for forming fluoride terminations on at least the surface of the oxide layer. In some embodiments, the fluorinating agent includes one or more of HF, _NF3 , plasmas thereof, or combinations thereof. In some embodiments, the fluorinating agent consists essentially of HF. In some embodiments, the fluorinating agent does not substantially contain HF. In some embodiments, the fluorinating agent consists essentially of _NF3 .

As used in this regard, a reactant consists essentially of a specified species if, on a molar basis, it is greater than or equal to about 95%, 98%, 99%, or 99.5% of the specified species (excluding any diluents or other inert (non-reactive) species).

As used in this context, a reactant is substantially free of a stated species if the stated species comprises less than or equal to about 5%, 2%, 1%, or 0.5% of the reactant (excluding any diluents or other inert (non-reactive) species).

In some embodiments, the fluorinating agent comprises one or more of an organic fluoride, an organic oxyfluoride, a metal fluoride, or _a combination thereof. In some embodiments, the organic fluoride has the general formula _CxHyFz , wherein x is 1 _to 16, y is 0 to 33, and z is 1 to 34. In some embodiments, the organic _oxyfluoride has _the general formula _CxHyOwFz , wherein x is 1 to 16, y is 0 to 33, w is 1 to 8, and z is ₁ to 34.

In some embodiments, the metal fluoride has the general formula _MFz , wherein M is selected from one or more of molybdenum, tungsten, vanadium, niobium, titanium, or tantalum, and z is 1 to 6. In some embodiments, the metal fluoride comprises or consists essentially of MoF6, _WF6 , _VF3 , _VF4 , _VF5 , _NbF5 , _{TiF4 ,} or _TaF5 .

In some embodiments, the fluorinating agent is co-flowed with an additional gas. In some embodiments, the additional gas is selected from one or more of the following: O ₂ , N ₂ O, NH ₃ , or H ₂ .

After forming the fluoride layer, the fluoride layer 620 is exposed to a halide etchant to remove the fluoride layer 620. In some embodiments, the halide etchant is referred to as a metal halide. In some embodiments, the halide etchant includes one or more species of the general formula EX ₃ , wherein E includes one or more of aluminum (Al) or boron (B), and X includes one or more of Cl, Br, or I. In some embodiments, the halide etchant contains BCl ₃ or consists essentially of BCl ₃ .

In some embodiments, the halogenide etchant comprises or consists essentially of one or more species of the general formula _MXy , wherein M comprises one or more of Ti, Sn, Mo, W, or Nb, X comprises one or more of Cl, Br, or I, and y is 1 to 6. In some embodiments, the halogenide etchant comprises or consists essentially of one species of the general formula _MXy , wherein M comprises one or more of Ti, Sn, Mo, W, or Nb, X comprises one or more of Cl or Br, and y is 1 to 6.

In some embodiments, exposing the oxide layer to the fluorinating agent produces a fluoride layer that is, on average, at most one monolayer thick. Without being bound by theory, it is believed that surface termini of the oxide layer react with the fluorinating agent to produce fluoride termini on the surface of the oxide layer. The surface reaction is confined to the exposed surface of the oxide layer and affects only the top layer of atoms of the oxide layer. Therefore, in some embodiments, method 100 removes less than or equal to one monolayer thickness of the oxide layer.

In some embodiments, method 100 is repeated. After removing the bulk fluoride layer, a new layer of oxide layer is exposed. Method 100 may be repeated to remove a predetermined amount or thickness of the oxide layer.

Additional embodiments are directed to methods for removing etch residues or other contaminants from a metal oxide surface prior to performing the method 100 described above to etch the oxide layer. Referring to FIG. 1 and FIG. 4B , for these embodiments, the method 100 begins at operation 105, where contaminants 630 are removed from an oxide layer 610 on a substrate 600. Once the contaminants 630 are removed from the surface of the oxide layer 610, the method 100 continues as described above by exposing the oxide layer 610 to a fluoriding agent to form a fluoride layer 620, and exposing the fluoride layer 620 to a halogenide etchant to remove the fluoride layer 620.

In some embodiments, contaminants include carbon films or moisture on the surface of the oxide layer 610. Without being bound by theory, it is believed that these residues may interfere with the fluorination and removal of the oxide layer 610. In some embodiments, an etching process is performed prior to the disclosed method 100, resulting in etch residues or contaminants including moisture and/or carbon films.

In operation 105, etch residues or contaminants may be removed by exposing the substrate to a free radical cleaning process 630. In some embodiments, the free radicals of the cleaning process include one or more of H*, OH*, O*, or _H2O *. In some embodiments, the free radicals are generated by passing a free radical gas over a hot filament. In some embodiments, the free radicals are generated by forming a plasma from the free radical gas. In some embodiments, the plasma is generated by a remote plasma source.

Scheme 2 provides an exemplary reaction scheme for method 100 (including operation 105 ).

Scenario 2:

Surface with water/carbon + plasma → metal oxide (1)

Metal oxide + fluorine source → metal fluoride layer (2)

Metal fluoride layer + metal halide → volatile products (3)

4C, in some embodiments, method 100 selectively removes oxide layer 610 relative to other materials 640 on the exposed surface of substrate 600. In some embodiments, other materials may include or consist essentially of TiN, _TaN , SiN, _SiO2 , _Al2O3 , carbon-based materials, or combinations thereof.

In some embodiments, the selectivity of removing oxide layer 610 relative to other materials 640 is greater than or equal to about 5:1, greater than or equal to about 10:1, greater than or equal to about 15:1, greater than or equal to about 20:1, or greater than or equal to about 25:1.

In a specific embodiment, the alumina layer is etched by exposure to NF ₃ /H ₂ and BCl _3. The process is selective to TiN, SiN, SiO ₂ , Al ₂ O ₃ and carbon with a selectivity greater than or equal to about 20:1.

Additional embodiments of the present disclosure relate to methods that increase the selectivity of the method 100 described above by performing the method in a processing chamber that includes a nickel chamber material. In some embodiments, the nickel chamber material is found as part of one or more of the following: a processing kit, a showerhead, a susceptor, or a confinement ring.

As described above, the substrate 600 including the oxide layer 610 is exposed to a fluoriding agent to form a fluoride layer 620. The chamber is then rinsed. The fluoride layer is exposed to a halide etchant, and the chamber is rinsed again. This cycle can be repeated to remove a predetermined thickness of the oxide layer 610. The fluoriding agent and the halide etchant used can be any of the fluoriding agents and/or halide etchants described above.

The inventors have surprisingly discovered that when performed in a processing chamber comprising a nickel chamber material, an oxide layer is selectively removed over TiN, SiN, TaN, SiO, AlO, LaO and carbon, and silicon. In some embodiments, the selectivity for the oxide layer relative to silicon is greater than or equal to about 5:1, greater than or equal to about 10:1, greater than or equal to about 15:1, greater than or equal to about 20:1, greater than or equal to about 25:1, greater than or equal to about 30:1, greater than or equal to about 35:1, greater than or equal to about 40:1, greater than or equal to about 45:1, or greater than or equal to about 50:1.

Some embodiments of the present disclosure relate to various methods for removing metal oxide thickness greater than an atomic layer in a single process cycle. Referring to FIG. 2 and FIG. 4D , method 200 begins at operation 210 , where a substrate 600 including an oxide layer 610 is exposed to a fluoridation agent to form a bulk fluoride layer 650 having a thickness T.

The fluorinating agent used in the method 200 may be any of the fluorinating agents described above for the method 100. To achieve a depth of fluorination, in some embodiments, the fluorinating agent may further include _H2 .

In some embodiments, the bulk fluoride layer has a thickness of greater than or equal to about 5 angstroms, greater than or equal to about 10 angstroms, greater than or equal to about 15 angstroms, or greater than or equal to about 20 angstroms. In some embodiments, the bulk fluoride layer has a thickness in a range of about 5 angstroms to about 30 angstroms, or in a range of about 7 angstroms to about 20 angstroms, or in a range of about 10 angstroms to about 15 angstroms.

The method 200 continues at operation 220 by exposing the bulk fluoride layer 650 to a halide etchant to remove the bulk fluoride layer 650. The halide etchant used in the method 200 can be any of the halide etchants described above for the method 100. Scheme 3 provides an exemplary reaction scheme for the method 200 shown in FIG. 2 .

Solution 3:

Metal oxide + fluorine source → bulk fluoride layer (1)

Bulk fluoride layer + metal halide → volatile products (2)

Some embodiments of the present disclosure relate to methods of etching metal hydroxide materials instead of the oxide layer described above. Referring to FIG3 and FIG4E , method 300 begins at operation 310 by exposing oxide layer 610 to an oxidizing plasma to form a hydroxide layer 660 .

The hydroxide layer 660 can be formed by exposing the oxide layer to an oxidizing plasma. In some embodiments, the oxidizing plasma is a remote plasma. In some embodiments, the oxidizing plasma includes free radicals of one or more of: water, peroxide, alcohol, or a combination thereof. In some embodiments, the oxidizing plasma includes OH* free radicals.

The method 300 continues at operation 320 by exposing the hydroxide layer 660 to a fluorinating agent to form a fluoride layer 670. The fluorinating agent used in the method 300 may be any of the fluorinating agents described above with respect to the method 100.

The method 300 continues at operation 330 by exposing the fluoride layer to a halide etchant to remove the fluoride layer 670. The halide etchant used in the method 300 may be any of the halide etchants described above with respect to the method 100.

Scheme 4 provides an exemplary reaction scheme for the method 300 shown in FIG. 3 .

In some embodiments, method 300 is repeated to remove a predetermined thickness of oxide layer 610 and/or hydroxide layer 660 .

Solution 4:

Oxide layer + OH* group → oxide layer (A)

Hydroxide layer + fluorine source → fluoride layer (1)

Fluoride layer + metal halide → volatile products (2)

Throughout the specification, references to "one embodiment," "some embodiments," "one or more embodiments," or "an embodiment" mean that the particular features, structures, materials, or characteristics described in connection with the embodiment are incorporated into at least one embodiment of the present disclosure. Therefore, phrases such as "in one or more embodiments," "in some embodiments," "in an embodiment," or "in an embodiment" that appear throughout the specification do not necessarily refer to the same embodiment of the present disclosure. In addition, in one or more embodiments, the particular features, structures, materials, or characteristics may be combined in any suitable manner.

Although the present disclosure has been described with reference to specific embodiments, it will be understood by those skilled in the art that the embodiments described are merely illustrative of the principles and applications of the present disclosure. It will be apparent to those skilled in the art that various modifications and variations may be made to the methods and apparatus of the present disclosure without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure is intended to include modifications and variations within the scope of the appended claims and their equivalents.

100: Method 105,110,120: Operation 200: Method 210,220: Operation 300: Method 310,320,330: Operation 600: Substrate 610: Oxide layer 620: Fluoride layer 630: Contaminants 640: Other materials 650: Bulk fluoride layer

In order to understand in detail the manner in which the above-mentioned features of the present disclosure are achieved, the present disclosure briefly summarized above may be described in more detail by referring to some of the embodiments illustrated in the accompanying drawings. However, it should be noted that the accompanying drawings illustrate only typical embodiments of the present disclosure and therefore should not be considered as limiting the scope of the present disclosure, as the present disclosure may admit of other equally effective embodiments.

FIG. 1 is a flow chart of an exemplary method according to one or more embodiments of the present disclosure;

FIG. 2 is a flow chart of an exemplary method according to one or more embodiments of the present disclosure;

FIG3 is a flow chart of an exemplary method according to one or more embodiments of the present disclosure; and

4A-4E are cross-sectional views of an exemplary substrate during processing according to one or more embodiments of the present disclosure.

Domestic storage information (please note in the order of storage institution, date, and number) None Foreign storage information (please note in the order of storage country, institution, date, and number) None

100:Methods

105,110,120: Operation

Claims (14)

An etching process includes: exposing a substrate surface having an oxide layer thereon to a fluoriding agent to form a fluoride layer, the oxide layer consisting essentially of bismuth oxide; and exposing the fluoride layer to a halide etchant to remove the fluoride layer, the halide etchant including a compound having the general formula EX ₃ , wherein E includes aluminum (Al) and X includes one or more of Cl, Br, or I, wherein the substrate surface has at least one other material, the material including one or more of the following: TiN, TaN, SiN, SiO ₂ , Al ₂ O ₃ , or a carbon-based material, and the oxide layer is selectively etched prior to the at least one other material, and wherein the selectivity of the etching process is greater than or equal to about 10:1. An etching process as described in claim 1, wherein the fluorinating agent comprises one or more of the following: an organic fluoride having _the general _{formula CxHyFz} , wherein x is 1 to 16, y is 0 to 33, and z is 1 to 34; an organic oxyfluoride having _the general formula _CxHyOwFz , wherein x is 1 to 16, y is 0 to 33, w is 1 to 8, and z is 1 to 34; _a metal fluoride; or a combination of _the above substances. An etching process as described in claim 1, wherein E further includes boron (B). An etching process as described in claim 1, wherein the halide etchant includes a compound having a general formula MX _y , wherein M includes one or more of titanium (Ti), tin (Sn), molybdenum (Mo), tungsten (W) or niobium (Nb), and X includes one or more of Cl, Br, or I, and y is 1 to 6. The etching process as described in claim 1 further includes: repeatedly exposing to the fluoride agent and the halide etchant to remove the oxide layer of a predetermined thickness. The etching process of claim 1, wherein the fluoriding agent is co-flowed with hydrogen (H ₂ ) gas, and the fluoride layer has a thickness ranging from about 10 angstroms to about 15 angstroms. The etching process of claim 8, wherein the fluoride layer is formed in a processing chamber comprising a nickel chamber material. The etching process as described in claim 1 further comprises: before exposing the substrate surface to the fluorinating agent, exposing the substrate surface to a cleaning plasma, wherein the cleaning plasma comprises one or more of H*, OH*, O*, or H ₂ O*. An etching process as described in claim 8, wherein the cleaning plasma removes a carbon film and/or moisture from the surface of the substrate. An etching process as described in claim 9, wherein the carbon film and/or moisture is a result of an etching process. An etching process includes: exposing a substrate surface having a hydroxide layer thereon to a fluoriding agent to form a fluoride layer; exposing the fluoride layer to a halide etchant to remove the fluoride layer, the halide etchant including a compound having a general formula EX ₃ , wherein E includes aluminum (Al) and X includes one or more of Cl, Br, or I; and exposing a substrate surface having an oxide layer thereon to a plasma to form the hydroxide layer, the plasma being formed from one or more of: H ₂ O, H ₂ O ₂ , or an alcohol. An etching process as described in claim 11, wherein the oxide layer is essentially composed of aluminum oxide. An etching process includes: exposing a substrate surface having an oxide layer and a second material to a fluoriding agent in a processing chamber including a nickel chamber material to selectively convert a portion of the oxide layer into a fluoride layer, the second material including one or more of the following: TiN, SiN, TaN, SiO, AlO, LaO, carbon, silicon, or a combination thereof; and exposing the fluoride layer to a halide etchant to remove the fluoride layer, the halide etchant including a compound having a general formula EX ₃ , wherein E includes aluminum (Al) and X includes one or more of Cl, Br, or I. An etching process as described in claim 13, wherein the second material consists essentially of silicon and the etching process has a selectivity greater than or equal to about 20:1.